FORT HOOD, Tex. - Two Army Reserve troops at the center of the Abu Ghraib prisoner abuse scandal faced off in a military courtroom yesterday, with one describing from the witness stand harsh treatment by his fellow soldier that went beyond what the world saw in photographs.

Pvt. Ivan L. "Chip" Frederick described for the first time how Spc. Charles A. Graner Jr. allowed a hooded and handcuffed inmate to walk directly into a 6-foot-tall pole and, another time, elbowed in the head a detainee who was trying to help U.S. soldiers track two escapees from the troubled Iraq prison.

Testifying at the first contested trial in the far-reaching scandal, Frederick said Graner showed off a photograph he had taken of an Iraqi detainee baring her breasts and, during an incident documented in widely circulated pictures, boasted to his wartime girlfriend that masturbating detainees were a gift for her birthday.

Graner's trial, which opened yesterday in a packed military courtroom here, is the first test of claims by the low-ranking soldiers charged in the case that the abuses were led or directed by higher-ranking intelligence operatives who wanted detainees "softened up" for interrogations.

While Frederick said intelligence officers gave guards some instructions on the treatment of detainees, he and other members of the Western Maryland-based 372nd Military Police Company testified that there were no orders condoning the humiliating abuses and sexual poses photographed by low-ranking soldiers.

"We were being told to do things like handcuff them to the door. The things we were charged with - we weren't ordered to do those," said Frederick, a former staff sergeant who pleaded guilty in the scandal and was sentenced to eight years in military prison.

Graner's court-martial comes amid increasing evidence of prisoner mistreatment elsewhere in Iraq, as well as in Afghanistan and at the U.S. detention facility at Guantanamo Bay, Cuba. But prosecutors laid out yesterday a tightly focused case that concentrated on the events of one night in November 2003, involving inmates at Abu Ghraib who were not considered of value to intelligence operatives.

Maj. Michael Holley, the lead military prosecutor, told the 10-man jury hearing the Graner case that much went wrong at Abu Ghraib. But he said other problems, and other perpetrators, would be dealt with in other proceedings.

"It was a very chaotic environment," Holley said in his opening statement. "What we're presenting to you at this trial is the serious misconduct - the things that anyone would look at and say, 'That is beyond the pale.'"

Defense attorney Guy Womack countered that the images shown in the photographs - a detainee tethered to a leather leash, for instance, or naked and hooded prisoners piled in a pyramid - represented legitimate methods of controlling detainees and did not amount to abuse.

"Don't cheerleaders form pyramids all over the country?" Womack asked in his opening statement, in which he noted that parents sometimes use a leash to control a wandering toddler. "You've probably been at airports or shopping malls and seen children on tethers. They are not being abused."

Jurors heard testimony yesterday from three of the seven accused soldiers from the 372nd - Frederick, Pvt. Jeremy C. Sivits and Meghan Ambuhl, who is no longer in the military. All three testified as part of their plea deals with prosecutors.

Sivits, who is serving a one-year prison term, recounted seeing Graner punch a prisoner in the head on Nov. 7, 2003, the night that is the focus of the government's case.

"The detainee just kind of shook and lay there on the floor," Sivits testified. "I said to [then] Corporal Graner, 'I think you knocked him out, man.' And when I checked under the sandbag [covering the detainee's head], he was unconscious."

Another member of the 372nd, Spc. Matthew Wisdom, testified about stumbling upon the scene of the prisoners placed in pyramids. He said he was upset by what he saw and immediately reported it to his supervisor, Sgt. Robert Jones II, a member of the 372nd and Baltimore police officer in civilian life.

"It made me kind of sick," Wisdom said. "I didn't know what to do. It just didn't seem right."

But the focus of yesterday's testimony was Frederick, who, like Graner, had worked as a prison guard in civilian life before their Army Reserve unit was put in charge of prisoners at Abu Ghraib late last fall. Frederick, 38, and Graner, 36, were looked to as senior leaders in the unit before the abuse scandal.

Frederick acknowledged yesterday that he had punched a detainee in the chest the night of Nov. 7, 2003, and forced prisoners to masturbate while soldiers watched. In another instance, he admitted fondling the female detainee whom Graner photographed after Frederick said the 19-year-old prostitution suspect had approached him in a prison shower area.

But, under oath, Frederick denied any knowledge that the acts were carried out under instructions from higher-ranking officers or intelligence agents. Questioning Frederick about the night of Nov. 7, 2003, prosecutor Capt. Chris Graveline asked: "To your knowledge, had anyone in your chain of command ordered that these actions be taken against these seven detainees?"

"No, sir," Frederick responded.